Downsizing of internal combustion engines and increasing power requirements lead to higher engine specific output for boosted applications. As the requirements increase, the turbochargers must also increase flow capacity and boost levels to obtain higher performance levels (Hp). The increase in turbocharger size comes as a detriment to the low end performance metrics including surge, low end torque peak, and transient operation regimes including time-to-torque, and tip in acceleration.
The inventors herein have recognized the above-mentioned limitations and have developed a multi-spool turbocharger for an engine. In one example approach, a multi-spool turbocharger comprises a compressor including a plurality of single-rotating compressor spools and a turbine including a plurality of single-rotating turbine spools. In a second example approach, a multi-spool turbocharger comprises a compressor including a plurality of counter-rotating compressor spools and a turbine including a plurality of counter-rotating turbine spools.
Such a multi-spool turbocharger has the potential advantage of operating as a smaller turbine over a larger operating range, and in effect is “downsized” from a performance standpoint. Further, such multi-spool turbochargers can increase the flow capacity of a turbocharger without adversely affecting the low end performance metrics of the internal combustion engine. For example, such a multi-spool turbocharger may be used instead of a twin turbo system and may outperform the twin turbo system especially at the low end operating range of the engine.
Further, components of a multi-spool turbocharger can be scaled down relative to conventional turbocharger systems, leading to a potential reduction in the diameter or size of the turbocharger making it easier to package, a reduction in the mass of spools in the turbocharger leading to an increase in the surge margin, and a reduction of the inertia of each spool to allow it to accelerate easier to improving transient vehicle operation like acceleration and time-to-torque.
Further, each spool of a multi-spool turbocharger system can be designed to accomplish different tasks at different operating regimes in the engine system. For example, a two spool can be designed to have each spool operate in a similar regime to balance aerodynamic and mechanical loads in the system. The rotational speed of a spool may be controlled to spooled down or the airflow though a spool can be bypassed in the system to reduce engine pumping work, and increase the low end operating range of the engine further. Spools can be designed to target different tasks and replace complicated systems like supercharger/turbocharger combinations, e-boost systems, series sequential, and dual boost systems at substantial cost savings, reduced size, and packaging improvements.
Additionally, the concentric shafts of the multi-spool turbocharger may be made to rotate in opposite directions (counter-rotation). Such counter-rotation may result in the elimination of variable interstage stators or other flow modification components thus reducing flow losses in the turbocharger and increasing the energy output of the turbine.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.